Heater for insulators



A. O. AUSTIN May 3, 1932.

HEATER FOR INSULATORS Filed Dec. 11, 1929 INVENTOR Mg S a E N M w/wn A TO A M Patented May 3, 1932 .UNITED STATES,

PATENT OFFICE ARTHUR O. AUSTIN, OF NEAR BAIRBERTON, OHIO, ASSIGNOR, BYMESNE ASSIGNMENTS, 'TO THE OHIO BRASS COMPANY, OF MANSFIELD, OHTO, ACORPORATION OF NEW JERSEY HEATER FOR INSULATORS This inventionrelates'to heating means for insulators, and has for one of its objectsthe provision of a heating device which will prevent the accumulation ofmoisture or other conducting substance on the surface of the insulatortending to reduce the insulation afforded thereby.

a A further object is to provide heating means for insulators which willdepend upon the voltage in the transmission line and not require a heavycurrent in the transmission line for its operation.

A further object is to provide heating means for insulators which shallbe of improved construction and operation.

Other objects and advantages will appear from the following description.

The invention is exemplified in the combination and arrangement of partsshown in the accompanying drawings and described in the followingspecification, and it is more particularly pointed out in the appendedclaims.

In the drawings:

Fig. 1 is a somewhat diagrammatic elevation showing one embodiment ofthe present invention.

( Fig. 2 isa view similar to Fig. 1 showing another form of theinvention.

In transmission lines operating at high voltage; considerable difficultyis caused by heavy leakage currents to ground or by insulators arcingover where the insulators are subjected to fog or to chemical or dustdeposits. Line-s operating along the seacoast or along lakes where saltor other chemical depositsbecome heavy, are likely to are over,particularly when the insulators are subjected to fog or rain. In thevicinity of railroads, cement plants. coke ovens or otherlocations wherethere are discharges into the air. conditions are likely to be verysevere. Along railroad lines. insulators coated with a deposit arelikely to be subjected to heavy discharges of steam from the locomotivewhich greatly increases the leakage. and sometimes causes an arc toground interrupting the service. On many lines. the discharges on theinsulator, frequently cause radio disturbances.

The above considerations apply not only to transmission insulators ofeither the suspen-.

sion, strain or pin type, but also to bushings, bus insulators and otherinsulating supports; both on the line and at stations. Due to thepresence of spray ponds, very severe conditions frequently exist attheelectrical station. In many cases, the outer ends of bushingsprojecting from station walls or roofs have to be increased in size inorder to revent arcing under the more severe conditions existing in fogor rains.

It is well recognized that if the surface of the insulator can bemaintained in a dry condition the danger of arcing is greatly reduced oreliminated. Where the surface of the insulator can be maintained in adry condition,

heavy deposits do not cause trouble to the same extent as where they aredamp or wet. \{Vhere the surface is maintained in a dry condition, thedeposits apparently do not adhere so strongly to the surface,consequently, windor wind and rain tend to keep the surfaces cleanerthan where the surfaces are wet for a great portion of the time. This isprobably due, in part at least, tothe fact that the leakage current orcharging current flowing over the surface of the insulator is greatlyreduced where the surface is kept dry. This leakage or charging currentflowing over the surface undoubtedly forms new compounds with thedeposit in many cases, producing deposits which are highly conductingwhen damp or wet.

While it is recognized that maintaining the temperature of the insulatorabove the dew point will greatly improve the effective insulation of theinsulator and'reduce the danger of arcing to ground for a givenelectrical stress, it has been found diflicult and expensive to warm theinsulator, particularly where the line voltage is high, without loweringits effective insulation for lightning or other se- ,vere conditions.

In the present invention, an arrangement is employed which makes itpossible to provide an insulator of high length efficiency or arcingvoltage for abnormal conditions so that high electrical integrity may bemaintained for these conditions, and, at the same time, permits ofheating of-the Insulator to a it possible to provide high effectiveflashover voltage for very severe conditions, such as lightning, wherethe surface deposits do not necessarily affect the performance of the1nsulator to the same degree as'fog or damp sur- This applies tosuspension or dead end strings,

face under the normal operating voltage.

bushing insulators, tandem insulators or other types of insulation.

In transmission lines operating at very high voltage and havingcomparatively small current flowing in the conductor, it is difficult toobtain the necessary energy for heating elements required to raise thetemperature of the insulating surface abovethe dew point.

The present invention secures the necessary heating of the this kind.

Although the invention is applicable to insulators for conditions ofpractically any transmission line voltage, it

is particularly applicable to transmission lines which are lightlyloaded .at the time when the most severe conditions are likely to beencountered. Many transmission systems are subjected to the most severeconditions in the early morning hours when the temperature is so lowthat the dew point is reached or severe fogs are encountered. 'At thistime of day, the current flowing in the main conductor is likely to berather small compared to the current during other portions of the day.If, therefore, dependence is placed upon the current flowing in theconductor to supply the energy for raising the temperature of theinsulator, and the energy utilized for heating is a direct function ofthe current flowing, the insulator may be greatly overheated part of thetime and receiving insuflicient heat at the time when. it is mostneeded. If, however, as in the present invention, the heating current isa function of the voltage or potential of the conductor, the conditionofithe insulator or the heat dissipated in the insulator will not dependupon the current flowing in the line and will not depend upon theloadingof the line. It is evident that conditions may exist where it isdesirable to be able to heat the insulator either proportionally to thecurrent flowing in the line or to the voltage. In general, however, atransmission line may be regarded as energized at all times so thatpotential can be depended upon to maintain a good condition of the surfface at all times. A combination method of heating, depending upon bothcurrent and voltage, could be used where a line had not been energizedfor some time, so that it would be impossible to raise the voltagewithout danger of causing flashover. Under a condition of this kind,itwould be possible to short circuit the line and cause a heavy current toflow through it at a comparatively low voltage. If a heating element,depending upon the flow of current, is available for raisingthetemperature of the insulator, a good operating condition can beestablished before it is necessary to raise the voltage. Lines subjectto heavy sleet storms some times are energized with a heavy circulatingcurrent, in order to melt the sleet from the conductors. At these times,the insulators could receive heat from a system, depending upon thecurrent to raise their temperature above the dew point or even to clearthem from accumulation of sleet.

Under normal operating conditions, the insulator heating systemdepending upon potential would maintain a good operating condition.\Vhile whole transmission systems may be equipped with insulator heatingmeans, it is usually necessary to heat the insulators in the vicinity,only, where unusually severe conditions exist or in the cities whereleakage or charging current causes complaints from observers notfamiliar with electrical phenomena.

Inthe embodiment shown in Fig. 1, the insulating element has aninsulating shell 10 with flanges 11. The insulating element is providedwith suitable attachments at either end. The attachment at the upper endpermits of attaching the insulator to one end of an ordinary insulatorstring or directly to a supporting tower, if desired. The attachment 13at the lower end permits the insulator to be attached to a clamp 14 ofsuitabledesign. The insulator may be of any suitable shape, the oneillustrated being filled with an insulating oil 15. The insulator ispreferably provided with a safety core 16 for maintaining the mechanicalreliability of the insulator or for taking the mechanical load imposedby the conductor where it is not desired to carry this load by means ofthe outer shell 10. The clamp 14 carries the main conductor 17 andanother conductor 18 is strung parallel to the main conductor 17. Thisconductor 18 is insulated from the main conductor by suitableinsulation. If a hollow conductor 17 is used, as shown in the drawings,the conductor 18 may be run inside of the conductor 17 and insulatedfrom same by any suitable insulation, as the voltage between the twoconductors need not be high. Heating elements 20 placed at any suitablelocation in theinsulating shell are electrically connected to theconductors 17 and 18.

The conductors 17 and 18 are connected to the secondary 21 of atransformer having a primary 22. One end of the primary 22 of thetransformer is connected to either conductor 17 or 18,'it beingillustrated as connected to 17. The other end of the primary 22 l isconnected to a suitable high voltage condenser 25, as shown in Fig. 2,or to a conductor 23 insulated from'the main conductor 17 by insulators24 and thus forming a condenser of which the conductors 17 and 23 arethe conductor elements separated by thejdielectric element 24. \Vhere aconductor 23is used, it must be so located that it will take up aportion of the charging current normally flowing between the mainconductor 17 and ground or between the main conductor and otherconductors. An appreciable portion of the charging current betweenconductor 23 and other conductors or between this conductor and groundmay be caused to flow over the primary 22 of the step-down transformer.The current flowing'between the conductors 17 and 23 will depend uponthe difference in potential between the two conductors and impedance inthe transformer circuit as well as the leakage over the insulatorsseparating the two conductors. \Vhile in general a comparatively highvoltage may be obtained, the amount of current flowing is entirely toosmall to apply to heated elements for practical purposes. Itis,therefore, advisable to provide a step-down transformer so that theamount of current flowing to the heated elements may be increased andthe voltage reduced. This applies whether the current flowing throughthe primary of the stepdown transformer is due to attaching a suitablecondenser or capacitor or a conductor 23. Where a conductor 23 is usedfor energizing the primary of the transformer, the cost of the step-downtransformerwill be a very appreciable part of the cost of theins'tallation. It is therefore advisable to reduce the number of thesetransformers par- 'ticularly as the out-put of the transformer will notbe increased materially with an increase in size.

VVhre a single transformer is used to supply current for the heatingelements for several insulators, it is necessary to supply a conductorfordistributing the energy of the secondary to the various insulators.In this case, one side of the transformer secondary is attached to thecondugtor 18, and the other side to the conductor ll. The heatingelements may then be tapped off from these two conductors at anysupport. In general, the conductor 23 need be supported only at the maininsulator supports. In the illustration, the conductor 23 is suspendedbelow the conductor 18 but in some cases it may be desirable to supportthe conductor 23 between the main conductor 18 and the tower. This willgive a greater insulation for the main conductor provided by theinsulators 24 for separating the conductors 18 and 23. It is notnecessary that a uniform distance be provided for the conductors, andthe conductor 23 may be placed above as well as below the mainconductoror to one side, if desired. This conductor 23 may be fairly close to themain conductor at the point of support or placed in a suitable locationso that clearance to ground, due to the presence of a cross arm or tothe swinging of an insulator under wind, will not be seriously reduced.Where the current flowing between conductors 17 and 23 is used toenergize the primary of the transformer, the only direct leakage pathsto ground from the conductors operating at high volta e will-be over themain insulator strings. here condenser elements 25 are used, it may benecessary toprovide an increase in insulation for these elements so thatthey will not are to ground under severe weather conditions. In someinstances, it may be advisable to place a primary 26 of a step-downtransformer in the conductor at the ground side of the condenser. Asuitable secondary 27 may be used to energize slightly a heating element28 for at least a portion of the condenser. I

If desired, the transformer having the primary 22 may be equipped with asecondary 29 for heating the upper end of the condenser in any suitablemanner. It is evident that the high voltage transformer may consist of aseries of auto transformers in place of having primaries andsecondaries. In this case, suitable taps are provided on the secondarycoil 22. The end coils will, of necessity, be provided with coils ofsuitable current carrying capacity.

It will be seen that an arrangement of the kind shown will make itpossible to supply energyior warming the insulator at all times whenthere is voltage on the system. If desired. the insulators may beequipped with a simple form of thermostat which will shortcircuit theresistance elements 20 when a sufliciently high temperature is reached.Such a thermostat isshown at the point 30. Wherea thermostat isused,heating means which will dissipate more-energy, can be used moreeconomically than where no thermostat is used. Where the thermostat isused, when the insulators become hot in the sun, the thermostat willprevent unnecessary loss of energy. In many cases, however, the energyis of such small importance compared to reliability that control meansfor heating the insulators would not be necessary. \Vhere the energizingconductor covers a very long stretch of line, suitable means may be provided for shunting the transformer primary or secondary, as desired, inorder to save energy when heating the insulators is not necessary. Any.suitable form of manual control, as a switch 31 or a remote controlsystem of suitable design, may be used.

In addition tothe manual control switch 30, an automatic relay circuitmay ,be' provided depending for its operation on the humidity of theatmosphere near the insulator. This control comprises a relay switch 31biased to closed position and arranged to be opened when current flowsin the control circuit. The circuit includes aswitch biased to closedposition but held open, when 3 the atmosphere is dry, by a strip or bar34 current to said capacitance member, and a heating element for saidinsulator energized by said conductor.

2. The combination with a transmission line, of an insulator forsupporting said line, a capacitance member associated with said line andarranged to be charged by the voltage of said line, a conductor forsupplying charging current to said capacitance member, a step-downtransformer having the primary thereof energized by said conductor, anda heating element for said insulator supplied with current from thesecondary of said transformer.

3. The combination with a transmission line, ofan insulator for saidline, a supplemental conductor extending along said line and insulatedtherefrom, a transformer for maintaining a difference of potentialbetween said line and conductor, and a heating element for saidinsulator, said heating element having itsterminals connected respectively with said line and conductor.

4. The combination with a transmission line, of-a conductordisposedalong said line andinsulated therefrom, a capacitance member arranged tobe charged by said transmissionline, a tap for supplying chargingcurrent to said capacitance member, a transformer having its primarywinding energized by said tap, the secondary of said transformer havingits terminals connected respectively with said transmissipn line andconductor, and a heating element for said insulatorhaving its terminalsconnected respectively with said transmission line and conductor.

5. The combination with a transmission line, of a conductor extendingalong said line and forming with said line the elements of a condenser,a second conductor extending along said line and insulated from saidfirstnamed conductor, and means energized by the charging current ofsaid condenser for supplying current to said second named conductor, anda heating element for said insulator electrically connected with saidsecond named conductor.

6. The combination with a transmission line, of an insulator forsupporting said line, a capacitance conductor extending along said lineand insulated therefrom, a supplemental conductor extending along saidline and insulated therefrom, a step-down transformer having its primaryconnected between said transmission line and conductor, the secondary ofsaid transformer having its terminals connected respectively with saidtransmission line and supplemental conductor, and a heating elementhaving its terminals connected respectively with said transmission lineand supplemental conductor.

7. The combination with a transmission line, of an insulator forsupporting said line, a supplemental conductor extending along said lineand insulated therefrom, a condenser electrically connected between saidsupplemental conductor and ground, a stepdown transformer having itsprimary winding electrically connected in series in the connectionbetween said supplemental conductor and ground, the secondary of saidtransformer having its terminals connected respectively with saidtransmission line and supplemental conductor, and a heating element forsaid insulator, said heating element having its terminals connectedrespectively with said transmission line and supplemental conductor. a

8. The combination with an insulator, of a heating element forevaporating moisture from the surface of said insulator, means forsupplying energy to said heating element, and

means controlled by atmospheric humidity for controlling the supply ofenergy to said A heating element, said means being arranged to supplyenergy when the air contains a predetermined degree of humidity and tocut off the supply of energy when theair is comparatively drier.

9. The combination with an insulator, of a heating element for saidinsulator, means for supplying energy to said heating element,

and means controlled by the humidity of.

the atmosphere for controlling the supply of energy to said heatingelement.

10. The combination with an insulator, of a heating element for saidinsulator, and means controlled by the humidity of the atmosphere towhich said insulator is subjected for automatically supplying energy tosaid heating element when the humidity of the atmosphere reaches apredetermined amount.

11. The combination with a transmission line, of an insulator forsupporting said line, a heater for said insulator, means for divertingenergy from said line for energizing said heater, and means controlledby humidity of the atmosphere for control-lin the supply of energy fromsaid line to sai heater.

In testimony whereof I have signed my 5 name to this specification this9th day of Dec., A. D. 1929.

ARTHUR O. AUSTIN.

